1. Field of the Invention:
This invention relates to a water discharge device for use with irrigation systems.
2. Description of the Prior Art:
Conventionally, irrigation of a farm is generally performed by employing a pipe formed with small openings therealong, said small openings each being adapted to receive a small tube such as a vinyl tube through which water is released preferably in the form of drops. In this kind of irrigation system, water is supplied through the pipe at a relatively low pressure to avoid too quick discharging of water. However, when such an irrigation pipe supplying water at a relatively low pressure is to be extended over a relatively long distance to operate with a number of small openings formed therealong, the pressure at the end portion of the pipe becomes very low, substantially reducing the water flow from the end portion of the pipe. Furthermore, since in the conventional irrigation system, each water supply port formed by the small vinyl tube is directly connected to the main supply pipe with no interposition of pressure reducing means, the unbalance of water flow rate along the length of the pipe becomes very large and the flow through each water discharge port fluctuates very largely according to small fluctuations of the pressure in the main pipe.
In order to avoid the large unbalance of water discharge rate along the length of the pipe in the conventional irrigation system, it is proposed to use a water discharge device as shown in FIG. 1, incorporating a pressure reducing structure so that the water pressure in the main pipe is kept at a relatively high level with no danger of discharging water at a too high rate. The water discharge device shown in FIG. 1 comprises a tubular element 1 having a connecting end portion 2 adapted to be inserted into an end portion of the hose. In the tubular element is inserted a screw element 3 also having a connecting end portion 4 of the same structure as the connecting end portion 2 of the tubular element 1, the screw element being formed with square threads 5 at the outside surface thereof. The screw element 3, as engaged into the mating grooves of tubular element 1, cooperates with the inside surface of the tubular element to provide a helical groove 6 communicating at one end thereof with a main passage 7 formed through the water discharge device by way of an annular opening 8 left between a counterbored portion of the tubular element and an end of the screw element 3, said groove 6 opening at the other end thereof to the outside of the water discharge device to provide a water discharge port 9.
By employing the water discharge device as shown in FIG. 1, water for irrigation or a mixture of water and a liquid manure fed at a relatively high pressure such as 1 - 2 Kg/cm.sup.2 through the passage provided by several pieces of the water discharge devices as well as several pieces of hoses connecting the water discharge devices is partly and gradually leaked out of the passage through the helical groove 6 to be moderately discharged out of the water discharge port 9. Since in this case the water pressure in the main supply pipe is kept at a high level and the water is reduced of its pressure at each water discharge device to produce a moderate water discharge flow from each water device, the unbalance of water flow rate between root and tip portions of the main water flow passage is small, making it possible to apply uniform irrigation to the entire region of the farm.
However, the conventional water discharge device as shown in FIG. 1 has the following drawbacks:
a. Since the tubular element and the screw element are assembled together to provide the water discharge device, clearances are apt to be formed between the fitting surfaces due to external causes, such as mechanical forces or hydraulic pressure, and if such clearances are formed, much amount of water under the pressure of 1 - 2 Kg/cm.sup.2 shortcuts the clearance, causing too high discharging rate of water. It is almost impossible to avoid the formation of such clearance, and since such clearances are formed in a very irregular manner, the unbalance of the water discharging rate is very large.
b. Since the depth of engagement between the tubular element 1 and the screw element 3 can not be readily adjusted, the resistance of the groove 6 or the water discharging rate can not be easily controlled. If the screw element 3 is fixedly mounted into the tubular element 1 to avoid the formation of the abovementioned clearances, it becomes difficult to disassemble the device to take out the screw element 3 from the tubular element 1 for the purpose of cleaning.